GB2230875A

GB2230875A - Fuel injection control system for automobile engine

Info

Publication number: GB2230875A
Application number: GB9009253A
Authority: GB
Inventors: Hiroshi Hosaka
Original assignee: Fuji Jukogyo KK; Fuji Heavy Industries Ltd
Current assignee: Subaru Corp
Priority date: 1989-04-28
Filing date: 1990-04-25
Publication date: 1990-10-31
Anticipated expiration: 2010-04-25
Also published as: GB9009253D0; US5068794A; GB2230875B; DE4013661A1; DE4013661C2; JPH02286851A

Abstract

To prevent the mixture becoming too rich or lean on acceleration or deceleration, the quantity of air induced into a cylinder during the intake stroke is estimated at 16-18 based on measures of throttle position alpha , engine speed N and perhaps air temperature @ measured before the intake stroke. The estimate @ap is used by injection calculating means 22, 24, possibly with feedback from an a/f ratio sensor 9, to calculate a fuel injection quantity @i which is injected immediately. Units 19-21 similarly calculate the actual air quantity induced Map during the intake stroke, and another fuel injection quantity Ti is calculated. If Ti > @i and @i < T180 then an asynchronous injection of the difference quantity DELTA Ti is carried out during the intake stroke. …<IMAGE>…

Description

.I - ' - -v L 1 1 FUEL INJECTION CONTROL SYSTEM FOR AUTOMOBILE ENGINE The

present invention relates to a fuel injection control system for an automobile engine to calculate a fuel injection quantity from an air induced quantity in cylinders of the engine in dependency on a throttle opening degree and an engine speed.

Generally, in the fuel injection control system of the type described above, a basic injection quantity Tp is first calculated with an induced air quantity and an engine speed as parameters and an actual fuel injection quantity Ti is then calculated by correcting the basic injection quantity TD with various factors for the correction.

The induced air quantity is measured by an induced air quantity sensor arranged on a directly downstream side of an air cleaner in a L-jetronic system. On the other hand, the induced air quantity is estimated in resDonse to the throttle opening degree (a) and the engine speed (N) in a so-called "ci- N" system. The "a-N" system makes simple or compact the engine unit and, hence, is superior in economical view to cause less fault. In these advantageous view points, the "Q-NII system is widely used for various types of the engine units.

The air quantity induced into the cylinder has a time-lag of first order with a certain time constant.

The time-lag of first order occurs according to a lag of changing an intake manifold with air. The induced air quantity estimated in response to the throttle opening degree and the engine speed at a transient state takes a value larger than an actua 1 air quantity in the cylinder and, hence, an air-fuel ratio becomes rich when the throttle valve is rapidly opened at the transient state.

1 2 Particularly, in an MPI (multi-point injection) type engine, a calculating timing of the fuel injection quantity supplied into the respective cylinders is set just before the intake stroke, that is an intake valve is about open. So that, at the transient state wherein the induced air quantity is changed during the intake stroke, there causes a difference between the induced air quantity at the calculation timing of the fuel injection quantity and the air quantity in the cylinder at the completion of the intake stroke. The difference adversely affects on airfuel ratio control characteristics.

In order to obviate such defect, the Japanese Patent Laid-open Publication No. 60-43135 discloses a system wherein an actual air quantity induced into the cylinderis estimated in dependency on the throttle opening degree at the initial stage of the transient state and the engine speed. The fuel injection quantity is changed with the time-lag of first order, so as to reach the fuel injection quantity corresponding to the estimated induced air quantity. Thus, an improvement in the air-fuel ratio control characteristics is attempted.

However, in the described prior art, there is no disclosure of means for estimating the required induced air quantity in dependency on the throttle opening degree and the engine speed.

In another aspect, in a prior application of the same applicant of the present application (Japanese Patent Application No. 63-257645), there is disclosed a system wherein an induced air quantity at this moment is first obtained in dependency on the throttle opening degree and the engine speed. Then the obtained air quantity is corrected by the correction factor set in independency on the subtracted difference between the obtained air quantity and the preliminarily obtained air quantity. Thus, the intake air quantity apptoximate to 1 1 3 the actual air quantity induced in the cylinder obtained.

Namely, as shown in Fig. 7, an estimated intake air quantity Map set at a fuel injection point A of the first cylinder of BTDCeO (for example, BTDC 800CA) before the intake stroke an induced air increasing quantity Map at an intake stroke completion point B is primarily estimated in dependency on the difference between an induced air quantity Map(tn) calculated from the throttle opening degree and the engine speed at the point A and the induced air quantity Map(tn-1) in the preceding cycle. A value obtained by adding the induced air quantity Map(tn) to the estimated induced air increasing quantity Map is the estimated induced air quantity Map at the fuel injection point A. A basic fuel injection quantity Tp is calculated from the estimated induced air quantity Mao and a desired air- fuel. ratio A/F as (Tp Map/A/F).

However, an acceleration of an engine equipped with more than four cylinders always starts on the intake stroke of certain one cylinder and, hence, aforementioned difference between the calculated air quantity and the actually induced quantity is caused in the present intake stroke of the certain cylinder. Therefore, an induced air quantity becomes lean by a quantity corresponding to a portion shown with hatching lines in Fig. 8.

Such a difference will be also caused during a deceleration cycle as a reverse phenomenon.

As a result, the air-fuel ratio control characteristics at the initial stage of the transient state becomes worse and a good response is not achieved. moreover, the exhaust gas emission at the transient state becomes worse and, hence, a load to a catalyst increases.

An object of the present invention is to substantially improve defects or _disAdvantages encountered to the prior art and to p=ride a system for . 1 - 4 1 controlling fuel injection of an automobile engine capable of supplying fuel injection quantity corresponding to air quantity in a cylinder at the completion timing of an intake stroke even in an initial stage of a transient state as well as in a transient operation, thus improving a transient response and load applied to a catalyst.

This and other objects can be achieved according to the present invention by providing a system for controlling fuel injection of an engine having a cylinder, an intake passage, a throttle valve provided in the intake passage and a fuel injector. The system comprises: means for detecting a first engine speed with respect to a.first reference crank angle before an intake stroke of the engine and a second engine speed with respect to a second reference crank angle on the intake stroke; means for detecting a first throttle opening degree with respect to the first reference crank angle and a second throttle opening degree with respect to the second reference crank angle;. means for estimating a throttle opening degree and an engine speed in accordance with the first throttle opening degree and the first engine speed; means for calculating a first air quantity in the cylinder during the intake stroke with the first throttle opening degree and the first engine speed; means for calculating a first air quantity in the cylinder during the intake stroke with the first throttle opening degree and the first engine speed; means for calculating a second air quantity in the cylinder in accordance with the second throttle opening degree and the second engine speed; means for calculating a first fuel injection quantity in accordance with the first air quantity in the cylinder and a second fuel injection quantity in accordance with the second air quantity in the cylinder calculated by said air quantity calculating means so as to start the injection of the first quantity at the first reference crank angle; and means eor calculating 1 asynchronous interrupted fuel injection quantity in accordance with a difference value between the first and second fuel injection quantities calculated by said fuel injection calculating means so as to carry out the injection of the difference value at the second reference crank angle.

In a preferred embodiment of the present invention, the control system further comprises a unit arranged in association with the fuel quantity calculating means for setting an air-fuel ratio feedback correction coefficient and also comprises means for estimating a throttle opening degree and an engine speed in accordance with the first throttle opening degree and the first engine speed so as to transmit estimated results to the first air quantity calculating means.

According to the fuel injection control system of the engine described above, a throttle opening degree and an engine speed are primarily estimated with respect to the reference crank angle before the intake stroke and the estimated air quantity in the cylinder is calculated in the intake stroke with the estimated throttle valve opening degree and the engine speed as parameters. In addition, the air quantity in the cylinder is calculated in accordance with the throttle valve opening degree and the engine speed with respect to the reference crank angle on the intake stroke. The fuel injection quantities are calculated in accordance with the estimated air quantity in the cylinder-so as to start the injection at the crank angle before the intake stroke quantity in the cylinder. Another fuel injection quantities are calculated in accordance with the air quantity in the cylinder. The asynchronous interrupt fuel injection quantity is calculated on the basis of the difference between both the fuel injection quantities.

Accordinglyr it will be possible to supply the fuel.injection quantity corresponding to air quantity in the cylinder in the completion of the inta16e stroke even in _. - - -1, - .fi 1 6 an initial stage of the transient state as well as during the transient operation. Thus,, the transient response,. the exhaust gas emission and the load to be 'applied to a catalyst are improved.

The other objects and features of the present invention will become understood from the following description with reference to the accompanying drawings.

Fig. 1 is a block diagram of a fuel injection control system according to the present invention; Figs. 2A and 2B show flowcharts representing operatidnal sequences of the fuel injection control system; Fig. 3 is a schematic sectional view of an engine control system; Fig. 4 is a schematic illustration showing an intake state; Figs. SA to SE are time charts showing fuel injection timing; Figs. 6A to 6C are graphs representing changing characteristics of a throttle valve opening degree, an intake air quantity and an air-fuel ratio, respectively; Figs. 7A and 7B are graphs showing a fuel injection quantity estimation based on a conventional technology; and Fig. 8 shows a graph representing a delay of air quantity in a cylinder based on the conventional technology..

Figs. 1 to 6 represent one embodiment according to the present invention.

Referring to Fig. 3 showing a schematic arrangement of a fuel injection control system of an automobile engine, an engine 1 is pirovided with an intake port la 35. with which an intake passage 2 communicates. A throttle valve 3 is assembled in the intake passage 2, and an air chamber 2a is formed between the throttle valve 3 and the 7', Z - - - 4... - 7 1 intake port la. An air cleaner 4 is provided at an upstream side of the intake passage 2.

An intake air temperature sensor 5 is mounted to an expanded chamber of the air cleaner 4. A sensor 6 for detecting an opening degree of the throttle valve 3 is mounted thereto. An injector 7 having a nozzle directed to -the intake port la is arranged downstream of the intake passage 2.

The engine 1 is also provided with an exhaust port lb with which an exhaust pipe 8 communicates. A sensor 9 for detecting an air-fuel ratio is mounted to the exhaust pipe 8. A catalyst means 1:0 is disposed downstream of the air-fuel ratio sensor 9.

The engine 1 also includes a crank shaft lc to which a crank rotor 11 is mounted. A plurality of projections lla to lld are formed on the outer periphery of the crank rotor 11. A crank angle sensor 1.2 is arranged at a portion opposing to the crank rotor 11.

In Fig. 3, only the #1 clinder of the four-cylinder engine is shown. The projections lla and llb represent a reference crank angle e. (for example, 8. BTDC 80-CA) with respect to the #1 and #2 cylinders and the #3 and #4 cylinders, respectively. Accordingly, an opening angle between the projections lla and llb is 1800. An angle el is formed between the projections lla and llc and the projections llb and lld. An engine speed N is calculated from an angular speed by detecting the angle e..

The projection lla designates a reference crank angle REF1 before the intake stroke representing the fuel injection start timing with respect to the #1 and #2 cylinders. And the projection lla also designates a reference crank angle on the intake stroke with respect to the #3 and #4 cylinders. Furthermore, the projection llb designates a reference crank angle REF2 before the intake stroke representing the fuel injection timing with respect to the #3 and #4 cylinders and also designates a 1 8 reference crank angle on the intake stroke with respect to the #1 and #2 cylinders (see Figs. 5B and SC).

In Fig. 3, reference numeral 13 designates a control unit. A fuel injection control means 14 of the control unit 13 shown in Fig. 1 comprises estimating means 15, means 16 for calculating an estimated quantity of the air passing the throttle valve 3, means 17 for calculating an estimated pressure in the air chamber 2a, means 18 for calculating an estimated air quantity in the cylinder, means 19 for calculating an air quantity passing the throttle valve 3r means 20 for calculating a pressure in the air chamber 2a, means 21 for calculating an air - quantity in the cylinder, means 22 for calculating a reference fuel injection quantity, means 23 for setting an air-fuel ratio feedback correction coefficient, means 24 for calculating a fuel injection quantity, and means 25 for calculating an asynchronous fuel injection quantity (ATi).

A fuel injection quantity Ti and the asynchronous injection quantity ATi are set to the cylinders, respectively. The quantities (Ti, ATi) will be referred to with respect to the #1 cylinder hereunder for the sake of convenience.

Fig. 4 represents a model of an intake system.

Referring to Fig. 4, an air quantity per unit time dM/dt in the chamber 2a of the intake passage 2 is represented by a difference between an induced air quantity Mat (throttle valve passing air quantity) and an air quantity fed to the cylinder (air quantity in the cylinder).

The air quantity per unit time is represented as dM/dt = Mat - Map...M The equation of state in the chamber 2a is P-V = M.R.T...M.

1 z 1 1 9 1 where P: inner pressure V: inner volume M: air quantity R: gas constant T: intake air temperature From the above equations (1) and (2), an inner pressure per unit time dP/dt in the chamber 2a is calculated as dP/dt = R.T.(Mat - Map)/V...(3).

Assuming that the gas constant R and the inner volume V in the equation (3) above are constant, R-T/V becomes a function with respect to the intake air temperature T. Accordingly, the quantity of air Map in the cylinder can be calculated in accordance with the values of the throttle valve passing air quantity Mat, the chamber pressure P and the intake air temperature T.

The estimating means 15 in Fig. 1 operates in the following manner. An estimated throttle valve opening degree 6L(tn), and an estimated engine speed N(tn) after a delay time (Td) in response to a present throttle valve opening degree cL(tn) detected by the throttle valve opening degree sensor 6 as well as a present engine speed N(tn) detected by the crank angle sensor 12 are calculated in accordance with the following equation when a signal representing the reference crank angle (REF 1) before the intake stroke is output from a crank angle sensor 12 for detecting the projection lla of the crank rotor 11.

The delay time (Td) means a time lapsed for a predetermined period from an angle of the fuel injection start timing to an angle corresponding to the middle of the intake stroke so as to be calculated in dependency on the engine speed. Almost of the air quantity induced in the cylinder of the engine 1 is induced until,the middle of the intake stroke. z Td S(tn) = S(tn) + - (S(tn) - S(tn - 1)) t Td = f (N) where S: a or N t: calculation cycle tn the present 'cycle of time (tn-l): preceding cycle of time Namely, a variation of the throttle valve opening lo degree or a variation of the engine speed after a certain time is calculated in the second term of the right side in the equation (4) and the throttle valve opening degree a(tn) or the engine speed N(tn) after a certain time is estimated by adding the present throttle valve opening dbgree cL(tn) or the present engine speed N(tn) in the first term of the right side to the variation.

In a calculating element 16a of the throttle valve passing estimated air quantity calculating means 16, an estimated quantity of air Mat(tn) passing the throttle valve is calculated from the estimated throttle valve opening degree d(tn) and the engine speed N(tn) obtained by the estimating means 15 and an estimated pressure P(tn) in the chamber 2a calculated in the means 17 for calculating the estimated inner pressure therein.

Namely, the throttle valve passing estimated ai.quantity Mat(tn) is represented as Plat = C -A - T. ap a... (5) where C air flow quantity coefficient A air passage sectional area T: Reynold's number Pa: atmospheric pressure pa: atmospheric air density In the equation (5)r: with respect to the Reynold's number IF, when P/Pa > {2/(k+l))1/(K-1), 4 a 11 Fg' ( (7a k- 1 and when P/Pa < (2/(k+l))1/(K-1)p T = 2gk/(K+1)). (2/( +1)} 1/ (K-!) where k: coefficient g: air weight In the means 16 for calculating the throttle valve passing estimated air quantity, there are provided an air passage sectional area table TBA for storing the air passage sectional area A preliminarily obtained through experiment with the throttle valve opening degree a as a parameter. The means 16 also has flow quantity' coefficient map MPc for storing the flow quantity coefficient C obtained through experiment with the throttle valve opening degree a and the engine speed N as parameters. There are also provided a Reynold's number map MPT wherein the Reynold's number W is obtained through experiment with the inner pressure P and the atmospheric pressure Pa as parameters. However, in Fig. 1, the atmospheric pressure Pa is considered to be a normal pressure and only the inner pressure P is considered as a parameter.

In the means 16, the air passage sectional area A is read from the air passage sectional area table TBA with the estimated throttle valve opening degree a(tn), calculated by the estimating means 15. The air flow quantity coefficient C is retrieved from the flow quantity coefficient map MPc with the estimated throttle valve opening degree 6L(tn) and the estimated engine speed N(tn). The Reynold's number W is retrieved from the Reynold's number map MPW with the estimated inner pressure (tn) calculated by the means 17.

z 12 1 The air quantity Mat(tn) is calculated in the calculating element 16a in accordance with the equation -(5) on the basis of the air passage sectional area A, the air flow quantity coefficient C and the Reynold's number W.

The estimated pressure calculating means 17 is provided with a coefficien't table TB.R.T/V for storing a coefficient R-T/V obtained through experiment with an intake air temperature T and also provided with a calculating element 17a for calculating, with the intake air temperature T detected by the intake air temperature sensor 5, the estimated pressure (tn+l) in dependency on the coefficient retrieved from the coefficient table TB-R-T/V, the air quantity Mat(tn) calculated by the air q1antity calculating means 16, and the estimated air quantity Mat(tn) in the cylinder calculated by the means 18 for calculating the estimated air quantity.

In the means 18, the estimated air quantity Map(tn) is calculated in accordance with the following equation.

Map = D N. nv-P ---(6) 2.R.T where D: stroke volume (piston displacement) N: engine speed ilv: volumetric efficiency Namely, the coefficient D/2.R.T is considered to be a function of the intake air temperature T, so that the coefficient D/2.R.T can be preliminarily obtained through experiment from the coefficient table TB- D/2.R.T with the intake air temperature T. The volumetric efficiency qv is also preliminarily obtained through experiment with the engine speed N and the throttle valve opening degree cl and is then stored in the volumetric efficiency map MplIv.

The calculating means 18 is also provided with a calculating element 18a for retrieving the poefficient D/2-R-T from the coefficient table TB-?D/2-R-T on the 1 is 13 basis of the equation (6). The calculating element 18a retrieves the volumetric efficiency qv from the volumetric efficiency map MPilv with the engine speed N and the throttle valve opening degree a estimated in the estimating means 15. The calculating element 18a further calculates the estimated air quantity Map(tn) from the estimated engine speed N(n) and the estimated pressure P(tn) calculated in accordance with the program in the preceding cycle of time of the estimated pressure 10 calculating means 17.

The estimated air quantity Map(tn) is calculated in accordance with the following equation.

D Map(tn) = ---N- 77v-P(tn)... (6'.R.T The means 19 for calculating air quantity passing through the throttle valver the means 20 for calculating pressure in the chamber 2a, and the means 21 for calculating air quantity in the cylinder are also provided with the maps MPc, MPIP, MPilv and the tables TB A, TB-R-T/V, TB- D/2.R.T as provided for the respective calculating means 16, 17 and 18.

The respective calculating means 19, 20 and 21 shown in Fig. 3 perform the calculations in response to the throttle valve opening degree cL(tnl), the engine speed N(tn'), and the intake air temperature T at a time when the reference crank angle (REF2) signal on the intake stroke detecting the projection llb of the crank rotor 11 is output from the crank angle sensor 12. However, since the intake air temperature T has less displacement per unit time, a sampling cycle may be long in comparison with the engine speed N.

In the air quantity calculating means 19, the air passage sectional area A is retrieved from the air passage sectional area ta61e TBA with the throttle valve opening degree a(tn') - The air flow coefficient C is retrieved from the flow coefficient map MPc with the : 14 1 throttle valve opening degree a(tn') and the engine speed N(tn'). And the Reynold's number Tis retrieved from the Reynold's number map MPW with the pressure P(tn') detected by the pressure calculating means 20.

The calculating means 19 is provided with a calculating element 19a for calculating the throttle valve passing air quantit Mat(tn') in accordance with the equation (5).

In the means 20 for calculating the pressure in the chamber 2a, the coefficient RT/V is retrieved from the coefficient table TB-RT/V with the intake air temperature T. The calculating means 20 is provided with a calculating element 20a for calculating the pressure P(tn1+1) in accordance with the equation (3) in response tb the coefficient RT/V, the throttle valve passing air quantity Mat(tn') calculated by the calculating means 19, and the air quantity Map(tn') calculated by the calculating means 21.

In the calculating means 21, the coefficient D/2.R.T is retrieved from the coefficient table TB.D/2.R.T with the intake air temperature T. The volumetric efficiency ilv is retrieved from thle volumetric efficiency map MPilv with the engine speed N(tn') and the throttle valve opening degree cL(tnl). Accordingly the air quantity Map(tn') is calculated as follows in accordance with the equation (6) in response to the pressure P(tn') calculated on the basis of the proceeding program of the calculating means 20 and the throttle valve opening degree cL(tn').

D MapXnj 2.R.T. 1N. 7)v.P(tn' In the basic fuel injection calculating means 22, the basic fuel injection quantities Tp and Tp (Tp Map/A/F; Tp = Map/A/F) as 'the desired air-fuel ratio A/F are respectively calculated from the estImated air quantity Map (tn) and the air quantity Map(tn').

il The air-fuel ratio feedback correction coefficient setting means 23 reads the output signal from the airfuel ratio sensor 9 and sets the air-fuel ratio feedback correction coefficient K by the proportion-integration (PI) control.

The fuel injection quantity calculating means 24 carries out the feed back correction of the respective basic fuel injection quantities Tp and Tp calculated by the calculating means 22 in dependency an the air-fuel ratio feedback correction coefficient UB set by the air- fuel ratio feedback correction coefficient setting means 23 and calculates the fuel injection quantities Ti and Ti - (Ti = Tp.KFB; Ti = Tp.K.FB).

Fuel injection pulse signal is output based on the fuel injection quantity Ti to the injector 7.

In the asynchronous interrupt injection calculating means 25, the fuel injection quantities Ti and Ti calculated by the fuel injection quantity calculating,.means 24 are compared. In case of Ti < Ti and Ti < T180 (lapse time for the rotation of 1800CA), a fuel injection gignal corresponding to the difference ATi (ATi = Ti Ti) is transmitted to the injector 7.

To the contrary, in case of Ti > T180 or Ti > Ti, the interrupt injection is not carried out.

Namely, as shown in Figs. 5A to 5E, the regular fuel injection starts at a time when a signal representing the reference crank angle REF1 before the fuel induction stroke of the #1 cylinder is generated by the crank angle sensor 12. On the other hand, the asynchronous interrupt injection starts at a time when a signal representing the reference crank angle REF2 on the intake stroke is generated by the sensor 12. Both the reference crank angle signals REF1 and REF2 are output in accordance with the detection of the projections lla and llb of the crank rotor 11. Both the projections lla and llb have 1800CA phase as shown in Fig. 3. Accordingly, in a' case where the fuel injection quantity h is large-T than T180, the 1 1 16 asynchronous interrupt fuel injection cannot be carried out. In addition, the asynchronous interrupt fuel injection quantity ATi calculated from the difference between Ti and Ti cannot be calculated, even in a case where the fuel injection quantity Ti is less than T180, but the fuel injection quantity Ti is larger than the fuel injection quantity Ti. Therefore, in such case, the asynchronous interrupt fuel injection is not carried out.

The control sequence of the fuel injection control means 14 will be described hereunder with reference to the flowchart of Fig. 2.

Referring to Fig. 2A, at the step S101, when the signal REF1 of the reference crank angle before the intake stroke is output, the estimated throttle opening degree a(tn) and the estimated engine speed N(tn) are calculated in response to the opening -degree ci(tn) and the engine speed N(tn),, respectively..

At the step S102, the estimated air quantity Mat(tn) is calculated from the estimated throttle opening degree a(tn) and the estimated engine speed N(tn) calculated at the step S101 and the estimated pressure P(tn) calculated at the step S104.

Thereafter, at the step S103, the air quantity Map(tn) is calculated in accordance with the estimated throttle opening degree Q5(tn) and the estimated engine speed N(tn) calculated at the step S101, the intake air temperature Tr and the estimated pressure P(tn) calculated at the step S104 of the preceding program.

At the step S104, the present estimated pressure P(tn+l) is calculated in accordance with the intake air temperature T, the throttle valve passing estimated air quantity Mat(tn) calculated at the step S102,, andthe estimated air quantity ap(tn) calculated at the step S103.

Thereafter, at the step S105, the basicfuel injection quantity Tp for the basis of the desired air fuel ratio A/F preliminarily set is 6'alculated (1p = is 17 Map(tn)/A/F) in accordance with the estimated air quantity Map(tn) calculated at the step S103.

At the step S106, the fuel injection quantity Ti is calculated by correcting the basic injection quantity Tp calculated at the step 5105 with the air-fuel ratio feedback correction coefficient UB (Ti = Tp KFB). At the step S107, the fuel injection pulse based on the fuel injection

quantity i is output to the injector 7.

An interrupt processing of the asynchronous interrupt fuel injection quantity is prosecuted at the step S108 when the signal REF2 of the reference crank angle on the intake stroke is output.

The interrupt processing will be represented by the flowchart of Fig. 2B.

First, at the step S201, the air quantity Mat(tn') passing the throttle valve is calculated from the throttle opening degree a(tnl) and the engine speed N(tn') calculated at a time when the reference crank angle signal REF2 on the intake stroke, and the pressure P(tn') calculated at the step 203 of the proceeding program.

Thereafter, at the step S202r the air quantity Map(tn') is calculated from the throttle opening degree cL(tn') and the engine speed N(tn'), the intake air temperature Tr and the pressure P(tn') calculated at the step S203 of the proceeding program.

At the step S203, the present pressure P(tn+l) is calculated in accordance with the intake air temperature T, the throttle valve passing air quantity Mat(tn') calculated at the step S201, and the air quantity Map(tn') calculated at the step 5202.

Thereafter, the step proceeds to the step S204, the basic fuel injection quantity Tp for the basis of the desired air-fuel ratio A/F preliminarily set is calculated (Tp = Map(tnI)/A/F) in accordance 'With the air quantity Map(tn') calculated at the ste-S202.

1 18 At the next step S205, the fuel injection quantity Ti is calculated by correcting basic injection quantity Tp calculated at the step S204 with the air-fuel ratio feedback correction coefficient KPB (Ti = Tp KFB).

In accordance with the steps, the interrupt processing is completed.

The completion of the interrupt processing, back to the steps of the flowchart of Fig. 2A. at the step S109, the fuel injection quantity Ti calculated at the step S106 and the fuel injection quantity Ti calculated at the step S205 are compared. And in case of Ti < Ti, the next step S110 starts, whereas in case of Ti k Ti, the program is completed as shown in Fig. 2A.

At the step S110, the pulse cycle of the fuel injection quantity Ti calculated at the step S106 and the T180 (lapsed time for the rotation of 1800CA) are compared. In case of Ti 1 T180, the program is completed, whereas in case of Ti:S T180, the next step S111 starts. The asynchronous interrupt fuel injection quantity ATi (ATi = Ti - Ti) is calculated from the difference between the fuel injection quantities Ti and Ti.

At the step S112, the fuel injection pulse in accordance with the asynchronous interrupt fuel injection quantity Ti calculated at the step S111 is output to the injector 7.

As described hereinbefore, as shown with respect to the #1 cylinder in Fig. 5D, in a case where it is discriminated that the fuel injection quantity Ti estimated before the intake stroke becomes short as the calculation result of the fuel injection quantity T1 on the intake stroke, the interrupt injection of the fuel corresponding to the underquantity is carried out on the intake stroke.

As a result, as shown in Fig. 6C, the air-fuel ratio control characteristic in the transient stlate can be remarkably improved in comparison with the case where no 1 19 correction of the injection quantity is made on the intake stroke. In addition, as shown in Fig. 62, the intake air quantity in the transient state changes from the air quantity with delay to the air quantity substantially the same as the actually induced air quantity. Accordingly, the control characteristic of the ignition cycle set on the basis of the intake air quantity and the engine speed can be also improved.

While the presently preferred embodiment of the 10 present invention has been shown and described, it is to be understood that this disclosure is for the purpose of illustration and that various changes and modifications may be made without departing from scope of the invention as set forth in the appended claims.

4 1

Claims

CLAIMS 1. A system for controlling fuel injection of an engine having a

cylinder, an intake passage, a throttle valve provided in the intake passage and a fuel injector, comprising: means for detecting a first engine speed with respect to a first reference crank angle before an intake stroke of the engine and a second engine speed with resnect to a second reference crank angle on the intake Stroke; means for detecting a first throttle opening degree with respect to the first reference crank angle and a second throttle opening degree with respect to the second reference crank angle; means for estimating a throttle opening degree and an engine speed in accordance with the first throttle opening degree and the first engine speed; means for calculating a first air quantity in the cylinder during the intake stroke with the first throttle opening degree and the first engine speed; means for calculating a first air quantity in the cylinder during the intake stroke with the firstthrottle opening degree and the first engine speed; means for calculating a second air quantity in the cylinder in accordance with the second throttle opening degree and the second engine speed; means for calculating a first fuel injection quantity in accordance with the first air quantity in the cylinder and a second fuel injection quantity in accordance with the second air quantity in the cylinder calculated by said air quantity calculating means so as to start the injection of the first quantity at the first reference crank angle; and means for calculating asynchronous interrupted fuel injection quantity in accordance with a difference value between the first and second fuel injection auantities calculated by said fuel injeletion calculating m' 1 21 means so as to carry out the injection of the difference value at the second reference crank angle.

2. The system according to claim 1 further comprising; means arranged in association with said fuel quantity calculating means for setting an airfuel ratio feedback correction coefficient.

The system according comprising:

to claim 1 further means for estimating a throttle opening degree and an engine speed in accordance with the first throttle 1 opening degree and the first engine speed so as to transtnit estimated results to the first air quantity calculating means.

4. The system according to claim 3 further comprising: means for detecting a first intake air temperature with respect to the first reference crank angle and a second intake air temperature with respect to the second reference crank angle; said first air quantity calculating means further responsive to the first intake air temperature for calculating the first air quantity; and said second air quantity calculating means further responsive to the second intake air temperature for calculating the second air quantity.

5. The system according to claim 4, wherein said first air quantity calculating means comprises: a first calculator responsive to the throttle opening degree and the engine speed both estimated by said correcting meanzy the first intake air temperature, and an estimated pressure in the intake passage for 1 22 calculating an estimated air quantity passing the throttle valve; a second calculator responsive to the first intake air temperature, the estimated air quantity passing the throttle valve, and the first air quantity in the cylinder for calculating an estimated pressure in the intake passage; and a third calculator responsive to the throttle opening degree and the engine speed both estimated by said estimating means, the first intake air temperature, and the estimated pressure in the intake passage for calculating the first air quantity in the cylinder.

6. The system according to claim 4, wherein said second air quantity calculating means comprises: a fourth calculator responsive to the second throttle opening degree, the second engine speed, the second intake air temperature, and a pressure in the intake pressure for calculating an air quantity passing the throttle valve; a fifth calculator responsive to the second intake air temperature, the air quantity passing the throttle valve, and the air quantity in the cylinder for calculating a pressure in the intake passage; and a sixth calculator responsive to the second throttle opening degree and the second engine speed, the second intake air temperaturer and the pressure in the intake passage for calculating the estimated air quantity in the cylinder.

7. The system according to claim 1, wherein said asynchronous interrupted fuel injection quantity calculating means comprises:

a first comparator for comparing the first and second fuel injection quantities to output the difference value between both quantities when the first fuel z 23 injection quantity is smaller than the ' second fuel injection quantity.

8. The system according to claim 7, wherein said asynchronous interrupted fuel injection quantity calculating means further comprises: a second comparator for comparing the first fuel injection quantity with a set value to produce the difference value when the first fuel injection quantity is smaller than the set value.

9. The system according to claim 3, further comprising: means for storing various equations and coefficients to calculate the first and second air quantities with the signals representing the engine speed, the throttle opening degree and the intake air temperature.

10. A system for controlling fuel injection of an engine substantially as hereinbefore described with reference to and as shown in figures 1 to 6.

Published 1990 at The Patent Office, State House, 66.71 High Holborn, London WC1R4TYFurther copies maybe obtained from The Patent Office. Sales Branch. St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex tecliniques ltd. St Mary Cray. Kent. Con. 1187